The invention relates to a method and apparatus for rotating rotationally symmetrical containers, such as bottles, while transporting them on a conveying surface. The containers are transported under backup pressure and are guided during the transportation, for which the conveying surface has a guide device or a railing on each side.
In particular empty glass or plastic bottles are rotated about their axis for inspecting their side walls. A side wall inspection device is known from EP-A-0 415 154 with which the lateral guide devices consist of belts arranged on both sides of the conveying surface and driven at different speeds so that the empty bottles held between them are rotated about their longitudinal axis. That apparatus requires that the empty bottles have previously been separated or at least guided to the conveying surface free of backup pressure. Therefore, if the empty bottles are not arranged free of pressure, they must be separated.
The invention is based on the problem of enabling the rotation of containers conveyed under backup pressure about their longitudinal axis in a simple manner.
This problem is solved according to the method of the invention in that one of two consecutive containers is arranged offset stable to one side and the other stable to the other side seen in the direction of conveyance after the site at which the containers are to rotate.
The problem is solved within the scope of the apparatus of the invention in that a device is provided for the stable arrangement of one of at least two consecutive containers against the railing and the other container against the other railing in the direction of conveyance after the site at which the containers are to rotate.
Apparatuses are known from DE-C-843 973 and DE-C-922 519 for transporting empty bottles under backup pressure with which empty bottles are alternately offset to the left and to the right railing. However, with those apparatuses, disturbances that lead to a change in the position of a container from one railing to the other railing propagate from the exit end of the conveying device counter to the direction of transportation. Such a change in position then also leads to a reversal of the direction of rotation of the individual empty bottles so that a defined rotation of the empty bottles is not achievable.
According to the basic concept of the present invention, a stable arrangement of at least two containers at the left or, resp., right railing prevents such a disturbance and a change in the position of the individual containers caused by that from taking place after those containers.
All subsequent containers lie stable against one of the two railings and roll along the railing and against each other, the containers rolling alternately along the left and right railing with alternate direction of rotation.
An apparatus for transporting rotationally symmetrical containers is known from U.S. Pat. No. 2,725,138, the containers backing up at the end of the conveying surface and rolling along the side rails. At the end of the conveying surface, the containers are arranged at defined distances on a further transporting device by means of a star wheel. Upon being taken over by the star wheel, each container is pushed laterally against the same railing. Hence, the containers which were previously positioned at the other rail change their position. That change of position causes all subsequent containers likewise to change their position and therewith also their direction of rotation.
The conveying surface can be moving or fixed. Moving conveying surfaces are conveyer belts, chain link conveyers, air cushions, rollers and the like. Fixed conveying surfaces can be simple metal slideways on which the containers are pushed by means of backup pressure, the backup pressure can be produced by a star wheel or a seriesed chain link conveyer. In this context, the term "transporter" encompasses all these kinds of conveying surfaces.